Why artificial gravity is not possible?

[nismaratwork]

The point in question was: 'who wants to loiter near a huge source of energy that could go off if it failed'.

The answer being: we do it all the time. We get around in vehicles that, if they fail, will make us (and everyone near us) very, very dead. Yet we do it because we have grown up with the technology and are comfortable enough with its safety record to consider the risk minimal.

There is no 'absolute' in safety-comfort; it is entirely relative to our familiarity.

There's a reason that we don't store energy for cars in banks of flywheels (ok, more than one reason)...

We do everything in our power to make most cars survivable in a collision, and let's be honest... most cars don't send lethal shrapnel that can fillet a waiting crowd, and they rarely explode. In a way, I would say that this is the difference between filling your dirigible with helium, or hydrogen. Yeah, you're still hanging in a balloon orders of magnitude higher than you need to fall to your death, but do you have to hang by a giant fireball?

 

[nismaratwork]

... Dave.

...

Why are you pink?

 

[DaveC426913]

There's a reason that we don't store energy for cars in banks of flywheels (ok, more than one reason)...

We do everything in our power to make most cars survivable in a collision, and let's be honest... most cars don't send lethal shrapnel that can fillet a waiting crowd, and they rarely explode. In a way, I would say that this is the difference between filling your dirigible with helium, or hydrogen. Yeah, you're still hanging in a balloon orders of magnitude higher than you need to fall to your death, but do you have to hang by a giant fireball?

It's all relative. You are assigning subjective ideas of what's acceptable risk/safety versus what isn't.

We've decided that 500mph is safe enough for even the most frail of human beings. We don't think twice about it, yet a failure will make us very dead.

Ask cro-magnon if he feels that being flung through the sky ten times faster than a cheetah in a big fire-maker (what's a gas tank?) is safe. Ask cro-magnon if he feels that hanging by some strings (what's helium?) miles above the Earth is safe.

You look at this "black-hole technology" and see danger. You think it can't be harnessed and made safe beyond a certain degree of reliability. But it's simply relative to you comfort level.

 

[DaveC426913]

Why are you pink?

I don't know.

 

[tbwhel]

Your points are well taken. My knowledge of gravity is, I admit, fairly limited but there are a few things I think I should clarify. 1) If we are to spend any substantial amount of time in space we must produce our own oxygen and deal with the CO2 we produce. I am sure someone here will mention CO2 scrubbers but the reality of chemical reactions is that we don't know of a way to do that without some sort of net loss. So that leaves 2 real solutions. the first is some sort of organic method, maybe involving a plant that is very efficient at oxygen production, or we need to take enough supplies to go the whole trip. This makes me think that any long distance ship would be the size of a small moon or asteroid. In terms of the metal in clothing, I meant it more as an electro-magnetic attraction, not fero-magnetic, I have to believe that by the time we actually start spending several years in space and maybe even consider longer term stays, we will have a good enough knowledge of magnetism to localize it to a person and prevent us from sticking to to much.your issue with furniture would be solved by making the furniture plastic, which is advantageous since plastic is lighter than metal. In terms of the micro sun, It is just a thought, one that is probably impossible, but it addresses the issue of what to use as a power source. We would after all need massive amounts of power for both propulsion and life support. I would be interested to see what every one thinks of these points. Lastly I want to explain my gravity is magnetic idea. As I understand it what holds an atom together is magnetism, more specifically electo-magnetism. Some here might say that is incorrect but positive to negative is just another way of saying north to south. So if atoms are attracted to each other by electro-magnetic forces then is stands to reason that gravity is the accumulated attraction between two objects and that with sufficient energy one might be able to create an artificial attraction between two objects. This may be wrong logic but I figured I would clarify my thought process. I only ask that before you discount it you try thinking about it without being so locked into the standard rules. Imagine some flexibility and that maybe we don't actually have a complete understanding of physics.

 

[tbwhel]

one thought for storing energy in cars might be a combination of regeneration through wind and rotation. It may seem nuts but I wonder if anyone has tried to regenerate lost electricity by putting in small channels some air over micro wind turbines embedded in the car. Also it might be interesting to see how much energy we could recapture by using the energy generation methods for wind turbines on the wheels (ex: magnets embedded in the hub caps or rims with the coils somehow suspended on the outside of the wheels. I recognize that this isn't perfect but I have to imagine that we could greatly increase the range of an electric car by reducing the energy lost to just the energy required to accelerate. we might even gain a little on down hills since the motor wouldn't be consuming energy.

 

[DaveC426913]

As I understand it what holds an atom together is magnetism, more specifically electo-magnetism. Some here might say that is incorrect but positive to negative is just another way of saying north to south. So if atoms are attracted to each other by electro-magnetic forces then is stands to reason that gravity is the accumulated attraction between two objects and that with sufficient energy one might be able to create an artificial attraction between two objects.
...
This may be wrong logic but I figured I would clarify my thought process.

Pretty much all of the above is incorrect. Your thought process would be clarified by reading up on the four fundamental forces: gravity strong and weak nuclear forces and electromagnetism.

 

[DaveC426913]

...I wonder if anyone has tried to regenerate lost electricity by putting in small channels some air over micro wind turbines embedded in the car.
...
generation methods for wind turbines on the wheels (ex: magnets embedded in the hub caps or rims with the coils somehow suspended on the outside of the wheels.

Many, many people have suggested such things. Here's the problem: you don't get something for nothing.

Wind turbines work by resisting the flow of air. That resistance increases the drag of the car, making it have to work harder to move. Ultimately, your wind turbines are simply stealing energy from your engine.

Same with magnets. They work via resistance too. That resistance will have to be overcome by the engine. Your magnets are simply stealing their energy from the engine.

 

[nismaratwork]

It's all relative. You are assigning subjective ideas of what's acceptable risk/safety versus what isn't.

We've decided that 500mph is safe enough for even the most frail of human beings. We don't think twice about it, yet a failure will make us very dead.

Ask cro-magnon if he feels that being flung through the sky ten times faster than a cheetah in a big fire-maker (what's a gas tank?) is safe. Ask cro-magnon if he feels that hanging by some strings (what's helium?) miles above the Earth is safe.

You look at this "black-hole technology" and see danger. You think it can't be harnessed and made safe beyond a certain degree of reliability. But it's simply relative to you comfort level.

I don't disagree with a word you've said, I just believe that objectively:


One person hanging from a helium balloon = high risk of harm to self, low to others.
One person in a jet filled with fuel (and worst case ignition scenario), you could devastate anything from one person, to whole buildings.
One person with a black hole could, if something goes catastrophically wrong as per the previous 2 examples, presents a risk to our planet, and potentially more.

I see unavoidable danger in falls, and fire, but with current concepts of gravity and what it might be, I find it hard to imagine (which may be my problem) a more destructive engine from the perspective of anything living on a planet, ship, or station.

There is after all, a difference between the human capacity to perceive and accurately asses risk, and then there's the worst-case. This does assume that the very nature of such a black hole isn't fail-safe... maybe "off" or "kaboom" would cause it to dissipate... I'm definitely the cro magnon of this piece. That said, there seems to be a far greater intrinsic risk with something that may well be the face of universal heat-death... and even our current nuclear stockpile.

 

[nismaratwork]

I don't know.

You see now, this is the kind of thing that would seriously occupy my thinking!

 

[tbwhel]

I understand the drag aspect of the wind turbines on the car but I am curious as to how the magnets would steal energy from the engine. The energy required to spin the wheel is already being spent. So if we are attaching the magnets to wheels and suspending our coils next to it I am failing to see the resistance that the magnets would produce. I understand that there is some energy loss. You have to lose some of the energy but this is really just meant to reduce the amount lost over time. and when the car is in a glide or on a hill, where the engine is not in use, why could we not use the fact that the car is moving and the wheels turning to generate some power back. In the end you get a net loss, but maybe we can spread that loss out over a greater amount of time. I have tried to Google this topic but can't find any actual explanation or reason why this hasn't been tried. Every thing I have found has simply said it is a waste of time and not possible. But without testing it how can we know for sure. It would be such a cheap experiment that I see no reason not to do it. If I had a place and the technical know-how I would try it but I don't.

 

[cjameshuff]

I understand the drag aspect of the wind turbines on the car but I am curious as to how the magnets would steal energy from the engine. The energy required to spin the wheel is already being spent. So if we are attaching the magnets to wheels and suspending our coils next to it I am failing to see the resistance that the magnets would produce.

Because the current generated in the coils produces a magnetic field that opposes the motion of the magnets. This is the principle behind regenerative braking, you convert the motion of the car to electrical power. It's not a desirable effect when you're not braking.

 

[tbwhel]

one last question. I understand the idea now behind regenerative braking. but if the magnetic current produced by the coil was actual strong enough to stop the car outright then there would be no point in having brakes. therefor there must be some point where the energy produced is slightly greater than the energy needed to stop the car. so even if we are losing some energy, can we actually afford to give up the production of that energy? the car might slow down a little faster but we need that energy regeneration. It seems to me that we have already applied this in some extent in what you called regenerative braking. sorry to be so stubborn but it seems silly to give up any energy just because you think it is to trivial. Given the limits on batteries we need to figure out how to squeeze out as much energy as possible.

 

[cjameshuff]

Your points are well taken. My knowledge of gravity is, I admit, fairly limited but there are a few things I think I should clarify. 1) If we are to spend any substantial amount of time in space we must produce our own oxygen and deal with the CO2 we produce. I am sure someone here will mention CO2 scrubbers but the reality of chemical reactions is that we don't know of a way to do that without some sort of net loss. So that leaves 2 real solutions. the first is some sort of organic method, maybe involving a plant that is very efficient at oxygen production, or we need to take enough supplies to go the whole trip. This makes me think that any long distance ship would be the size of a small moon or asteroid.

Our moon is the size of a small planet, with 1/4th the land area of Earth, and still only has 1/6th Earth's surface gravity. Piling mass up is an extraordinarily inefficient approach to the problem.
And we do know ways to regenerate oxygen, with and without plants. Plants don't use some mysterious, unknown way to do it, and we have more direct ways to do the job using electrical power. Even if plants are used, the power plant and farms aren't going to mass enough to have useful surface gravity.

In terms of the metal in clothing, I meant it more as an electro-magnetic attraction, not fero-magnetic, I have to believe that by the time we actually start spending several years in space and maybe even consider longer term stays, we will have a good enough knowledge of magnetism to localize it to a person and prevent us from sticking to to much.your issue with furniture would be solved by making the furniture plastic, which is advantageous since plastic is lighter than metal.

What'll hold the furniture down, then?
We actually have a very good understanding of electromagnetism, it really can't be "localized" in the way you describe.

In terms of the micro sun, It is just a thought, one that is probably impossible, but it addresses the issue of what to use as a power source. We would after all need massive amounts of power for both propulsion and life support.

We would not need such large masses of equipment that it would have a substantial gravity field.

I would be interested to see what every one thinks of these points. Lastly I want to explain my gravity is magnetic idea. As I understand it what holds an atom together is magnetism, more specifically electo-magnetism. Some here might say that is incorrect but positive to negative is just another way of saying north to south. So if atoms are attracted to each other by electro-magnetic forces then is stands to reason that gravity is the accumulated attraction between two objects and that with sufficient energy one might be able to create an artificial attraction between two objects. This may be wrong logic but I figured I would clarify my thought process. I only ask that before you discount it you try thinking about it without being so locked into the standard rules. Imagine some flexibility and that maybe we don't actually have a complete understanding of physics.

The above is almost entirely wrong. We have an exceptionally good understanding of how both electromagnetism and gravity behave. Gravity is completely unaffected by electromagnetic charge or electromagnetic properties of materials, and electromagnetism doesn't care about mass. The only similarities between the two are superficial...they can both cause attractive forces.

Again, the problem's solved, with 1800's technology. Spin the spacecraft . No need to carry the mass of a planet around, no power-hungry and inconvenient magnetic clothes that only provide a rough simulation of gravity. Simple rotation with a large enough radius (easily achievable with tethers even today) can provide an effect that is indistinguishable from gravity except with rotation-sensitive instrumentation.

 

[cjameshuff]

one last question. I understand the idea now behind regenerative braking. but if the magnetic current produced by the coil was actual strong enough to stop the car outright then there would be no point in having brakes. therefor there must be some point where the energy produced is slightly greater than the energy needed to stop the car.

This simply does not follow. Brakes exist on cars with regenerative braking because there are limitations to how fast a generator can convert mechanical energy to electrical energy, and because magnetic braking is much less effective at low speeds. It certainly doesn't imply that you can create energy out of nowhere.

so even if we are losing some energy, can we actually afford to give up the production of that energy? the car might slow down a little faster but we need that energy regeneration. It seems to me that we have already applied this in some extent in what you called regenerative braking. sorry to be so stubborn but it seems silly to give up any energy just because you think it is to trivial. Given the limits on batteries we need to figure out how to squeeze out as much energy as possible.

It's not that the amount of energy to be gained is too trivial to bother with, it's that there's no energy to be gained. The energy required to keep the car from slowing down is greater than that recovered. The only thing your suggestion accomplishes is wasting more energy as heat by unnecessarily converting it from mechanical to electrical and back to mechanical, both of which involve losses.

 

[cjameshuff]

Flywheels actually aren't that improbable as an energy storage medium for vehicles. Composite flywheels disintegrate into a wad of hot fluff when they fail. You'd want counterrotating flywheels and some way to ensure that both fail simultaneously to avoid excessive torques on the casing, but they could be safely used in vehicles.

 

[nismaratwork]

A cat for a hat, a hat for a cat, but nothing for nothing. When you're in physics land, this is your mantra. There may be some moments where the hat and cat are in play and no one seems to have either, but at the end of the 'day', it has to be a fair trade. I would just add that magnetic brakes strong enough to stop a car at ANY speed ticketed in a given state would be very strong. I'm not sure you want something attracting everything ferromagnetic on the road directly to your tires... you're not driving a maglev train that can glide over (or smoosh) a nail on a well maintained track after all.

 

[nismaratwork]

Flywheels actually aren't that improbable as an energy storage medium for vehicles. Composite flywheels disintegrate into a wad of hot fluff when they fail. You'd want counterrotating flywheels and some way to ensure that both fail simultaneously to avoid excessive torques on the casing, but they could be safely used in vehicles.

In practice to deal with the torque you make a casing that becomes shrapnel in a worst case scenario, and the flywheels out of stronger materials. The reality is that gasoline is far less explosive and immediately dangerous (barring the perfect mixture with air) than the kind of flywheels you're talking about. Gasoline may burn your car down to the frame rails given time, but if you're whipping up your flywheel and that "hot fluff" starts flying, it could punch a hole in the engine block!

To be compact, light, and durable, can you imagine the strength of the materials needed for the flywheel, and given the amount of energy involved you'd need a casing like a vault. I believe you'd rapidly find that the safety requirements at this time would make it far too heavy, and to ignore safety would be... bad.

 

[mheslep]

Flywheels actually aren't that improbable as an energy storage medium for vehicles. Composite flywheels disintegrate into a wad of hot fluff when they fail. You'd want counterrotating flywheels and some way to ensure that both fail simultaneously to avoid excessive torques on the casing, but they could be safely used in vehicles.

Last I looked, for vehicles smaller than a bus, the flywheel mass is a prohibitively large fraction of the total vehicle mass.

 

[nismaratwork]

Last I looked, for vehicles smaller than a bus, the flywheel mass is a prohibitively large fraction of the total vehicle mass.

I really need to learn how to be more concise... care to teach me the Mheslep method? I babbled about vault casings for a paragraph when a sentence would have done... I'm feeling a bit dissapointed in myself. :tongue:

The good thing about something like a bus using a flywheel is that you can reasonably partition it from the passengers in a way you just can't with a standard sedan.

 

[mheslep]

I really need to learn how to be more concise... care to teach me the Mheslep method?

Heh, well one can fine much better examples than my posts on PF.

 

[cjameshuff]

To be compact, light, and durable, can you imagine the strength of the materials needed for the flywheel, and given the amount of energy involved you'd need a casing like a vault. I believe you'd rapidly find that the safety requirements at this time would make it far too heavy, and to ignore safety would be... bad.

I can imagine a simple cast aluminum or steel case, yes. The scaling laws make lightweight, small radius, very high rotation rate flywheels preferable. They are essentially spools of carbon fiber, kevlar, etc with a binder. When they fail, a great deal of energy is released, but there are no chunks of high momentum material that would tear a hole in a reasonably strong casing as you describe. Your claims of dangerous shrapnel are incorrect.

mheslep refers to older style flywheels, but is correct, the main reason they are not often used is the size required...not danger of them exploding. A small vehicle powered purely by a steel or aluminum flywheel would largely be flywheel. More modern high speed composite flywheels have more promise for small vehicles...even if they're still too large for a primary energy storage medium, their ability to rapidly accept and supply energy gives them potential for use as temporary storage for regenerative braking and acceleration...for example: http://www.flybridsystems.com/

In comparison, capacitors have terrible energy density, and batteries have relatively severe limitations on charge/discharge rate and cycle count.

 

[mheslep]

... and batteries have relatively severe limitations on charge/discharge rate and cycle count.

Well charge rate is a problem, best addressed by battery swaps I believe. Discharge rate (i.e. specific power) is sufficient, and cycle life in a thermally controlled battery appears to be on the order of 2000-3000X, full depth of discharge.

 

[nismaratwork]

I can imagine a simple cast aluminum or steel case, yes. The scaling laws make lightweight, small radius, very high rotation rate flywheels preferable. They are essentially spools of carbon fiber, kevlar, etc with a binder. When they fail, a great deal of energy is released, but there are no chunks of high momentum material that would tear a hole in a reasonably strong casing as you describe. Your claims of dangerous shrapnel are incorrect.

mheslep refers to older style flywheels, but is correct, the main reason they are not often used is the size required...not danger of them exploding. A small vehicle powered purely by a steel or aluminum flywheel would largely be flywheel. More modern high speed composite flywheels have more promise for small vehicles...even if they're still too large for a primary energy storage medium, their ability to rapidly accept and supply energy gives them potential for use as temporary storage for regenerative braking and acceleration...for example: http://www.flybridsystems.com/

In comparison, capacitors have terrible energy density, and batteries have relatively severe limitations on charge/discharge rate and cycle count.

The flywheel detonates, the casing and other bits of car become shrapnel... and that's a much bigger issue with a smaller radius, rapid flywheel. That energy release is happening inside a CAR, concentrated and trapped by its casing... I'm sorry, but that's a bomb.

 

[mheslep]

The flywheel detonates, the casing and other bits of car become shrapnel... and that's a much bigger issue with a smaller radius, rapid flywheel. That energy release is happening inside a CAR, concentrated and trapped by its casing... I'm sorry, but that's a bomb.

So's a gas tank. As pointed out above the composite flywheels more or less vaporize on failure, as I understand without much risk to escaping the case. I believe the problem there is economic - the high RPM requires a near vacuum and exotic bearings. Fine for NASA, not so much in a Ford.

 

[nismaratwork]

So's a gas tank. As pointed out above the composite flywheels more or less vaporize on failure, as I understand without much risk to escaping the case. I believe the problem there is economic - the high RPM requires a near vacuum and exotic bearings. Fine for NASA, not so much in a Ford.

I don't know... it doesn't take much melted casing to kill you... I would add again that gasoline is flammable when mixed properly with oxygen. Without a bomb or large fire you won't have all of the energy in the gasoline released at once... not so with a flywheel.

Then... there's the NASA grade engineering, but that makes this less fun to talk about. :)

 

[DaveC426913]

This is sort of going off track. The simple point is that we utilize a technology with a ubiquity proportional to how manageable it becomes.

Any powerplant capable of propelling a starship and all its occupants on an interstellar journey will have to harness far more than enough energy to vapourize everything in a medium sized volume if it fails.

This hypothetical black-hole-engine is no different. Worse case, it's mounted at the end of a ten mile long extension rather than a one-mile long extension.

 

[nismaratwork]

This is sort of going off track. The simple point is that we utilize a technology with a ubiquity proportional to how manageable it becomes.

Any powerplant capable of propelling a starship and all its occupants on an interstellar journey will have to harness far more than enough energy to vapourize everything in a medium sized volume if it fails.

This hypothetical black-hole-engine is no different. Worse case, it's mounted at the end of a ten mile long extension rather than a one-mile long extension.

I'm not sure that's necessarily true... consider VASIMIR for instance. I think my point about a black hole is that it can scale beyond our capacity to manage it by its very nature. Even antimatter would be devastating, but it would annihilate, killl everyone... the end! A black hole wouldn't explode... in fact it would persist and potentially GROW. I agree with you in general, but a black hole is a unique... object... and anything that has the capacity to scale between microscopic and galactic is fundamentally dangerous in ways no other technology I can think of is.

 

[thedeester1]

you could place the space station in one of the gravity neutrals. therefore you wouldn't need fuel to spin the station it would all be done by repulsing gravity and ceterfugal force! Could scarifice gravity for supplies by using thruster engines to move you to supplies that were launched into space...then you would have to find the neutral zone again...Maybe 90% of t he supplies would be fuel?

 

[thedeester1]

pardon my spelling but its very possible! Gravity as a force has to exist between all large objects and the math of the middle is key. Put an object in the neutral zone and it will spin at the rate to create gravity

 

[dkotschessaa]

Of course whatever means we come up (rather than the rotational solution) is going to have an effect on nearby bodies, i.e. earth, if we are talking about putting this thing in orbit. What crazy tidal effects might we expect? Surfs up?

-DaveKA

 

[cjameshuff]

you could place the space station in one of the gravity neutrals. therefore you wouldn't need fuel to spin the station it would all be done by repulsing gravity and ceterfugal force! Could scarifice gravity for supplies by using thruster engines to move you to supplies that were launched into space...then you would have to find the neutral zone again...Maybe 90% of t he supplies would be fuel?

pardon my spelling but its very possible! Gravity as a force has to exist between all large objects and the math of the middle is key. Put an object in the neutral zone and it will spin at the rate to create gravity

...where did you get this idea?
The only "gravity neutral" I can think of in Earth's neighborhood is the point where Earth's and the moon's gravity is equal, just a bit on the far side of the Earth-Moon L1 point. Gravity doesn't repel and an object placed at this location (or the nearby L1 point, where you can actually have a closed orbit, albeit an unstable one) won't start spinning on its own...not due to being at any sort of neutral point, anyway.

And aside from that "neutral zone" stuff not working at all as described, it sounds like you're suggesting saving the small amount of fuel needed to spin up the station by using massive amounts of fuel to chase supplies around this "neutral zone"...

 

[DaveC426913]

you could place the space station in one of the gravity neutrals. therefore you wouldn't need fuel to spin the station it would all be done by repulsing gravity and ceterfugal force! Could scarifice gravity for supplies by using thruster engines to move you to supplies that were launched into space...then you would have to find the neutral zone again...Maybe 90% of t he supplies would be fuel?

pardon my spelling but its very possible! Gravity as a force has to exist between all large objects and the math of the middle is key. Put an object in the neutral zone and it will spin at the rate to create gravity

Yeah, I don't know what you're getting at. This describes nothing in physics that I know of.

There are Lagrange points, but they don't cause any spinning.

 

[thedeester1]

...where did you get this idea?
The only "gravity neutral" I can think of in Earth's neighborhood is the point where Earth's and the moon's gravity is equal, just a bit on the far side of the Earth-Moon L1 point. Gravity doesn't repel and an object placed at this location (or the nearby L1 point, where you can actually have a closed orbit, albeit an unstable one) won't start spinning on its own...not due to being at any sort of neutral point, anyway.

And aside from that "neutral zone" stuff not working at all as described, it sounds like you're suggesting saving the small amount of fuel needed to spin up the station by using massive amounts of fuel to chase supplies around this "neutral zone"...

I got this off of Wikki...not the most reliable source I know...But its kinda what i was getting at...Im not a student of astro physics its kinda a hobby for a geek.

http://en.wikipedia.org/wiki/Lagrangian_point

other neutral gravity points must exist between all mass in the solar system and the universe...otherwise fast colapse would be occurring NOW.

 

[nismaratwork]

I got this off of Wikki...not the most reliable source I know...But its kinda what i was getting at...Im not a student of astro physics its kinda a hobby for a geek.

http://en.wikipedia.org/wiki/Lagrangian_point

You've utterly misunderstood everything I can imagine in regards to what Langrangian points are, based on what seems to be a complete lack of understanding of gravity. I would recommend some reading on those subjects.